A variety of transillumination devices having an integrated flat panel light source are known in the existing art. These are used for bright-field, dark-field and/or oblique illumination types.
JP 2003-75725 A shows a combined transmitted bright-field and transmitted dark-field illumination device in which it is possible to switch over between bright-field and dark-field illumination by corresponding application of control to numerous LEDs.
In particular for viewing low-contrast specimens, illumination with diffuse light is not sufficient to depict the relevant details. A variety of actions are known in the existing for increasing the contrast. The illumination method is of particular importance especially in stereomicroscopy, since it is used to generate contrasts on the object being viewed that make structures on the object more visible, or indeed visible at all.
U.S. Pat. Nos. 7,345,815 B2 and 7,554,727 B2 describe the use, in the context of bright-field illumination, of light-directing elements that control the illumination angle of the sample. The fact that the maximum field is always illuminated has, however, a negative effect on contrast.
DE 10 2004 017 694 B3 describes a segmentation of the light source, the position and gap width of a slit aperture being varied. Oblique illumination is possible. The rectangular shape of the slit is, however, not ideal for the circumstances in a stereomicroscope having the two observation channels at an angle to one another. Operability, and the construction of the slit aperture, also need to be improved.
It is therefore desirable to describe a maximally flat transillumination device for homogeneous illumination of a microscope, which device can be used for bright-field, dark-field, and/or oblique illumination.